The present invention relates general to nuclear power plants, and more specifically to the emergency systems of such power plants.
A nuclear power plant typically has a nuclear reactor and a reactor coolant system (RCS) for removing heat from the reactor and to generate power. The two most common types of reactors, boiling water reactors (BWRs) and pressurized water reactors (PWRs) are water-based. In a PWR, the heated water from the reactor is fed to an electricity generator having a secondary coolant stream boiling a coolant to power a turbine. In a BWR, the electricity generator has a turbine driven directly by the reactor coolant. The RCS section downstream of the electricity generators but upstream of the reactor typically is called the cold leg, and downstream of the reactor and upstream of the electricity generators is typically called the hot leg.
If a failure occurs in the RCS, in what is typically called a loss of coolant accident (LOCA), the nuclear core does not properly cool, temperature begins to rise in the reactor. The temperature of the fuel elements in the core rises and, if not checked, can cause melt and potentially void the reactor, releasing the melt into the containment building. LOCA accidents of both PWRs and BWRS may include a main steam line break (MSLB).
During a LOCA, a standard evolution of pressure and temperature inside the containment involves an increase in pressure to a few bars in 5-18 hours, with a maximum temperature around 150° C., which is reduced to atmospheric pressure and temperature in a few days. Nuclear power plants are designed to weather such an event with a considerable safety margin. The cooling process is based on the physical properties of water and air at those temperatures.
During a LOCA in a PWR, an emergency core cooling system (ECCS) can be activated to cool the reactor by providing additional water to the RCS. An ECCS typically thus includes a high-pressure pump such as a centrifugal charging pump/high pressure injection pump (CCP/HPIP pump) exiting into the RCS. This can pump water from the refueling water storage tank (RWST), such as an in-containment RWST (IRWST), or a containment sump into the cold leg of the RCS. A volume control tank receiving water passing through a heat exchanger from the RCS cold leg can also provide water to the CCP/HPIP pump. A similar ECCS typically is present in BWRs where volumes of water existing in stand-by are actively or passively passed through the core in case of a LOCA accident.
The ECCS also typically has a low-pressure pump, such as a residual heat removal or safety injection system pump (RHR/SIS pump), which can provide water from the RWST or containment sump to the PWR or BWR reactor vessel, as well as water to a containment spray system. A heat exchanger is typically provided after the RHR/SIS pump, and heated water coming form reactor is passed through the heat exchanger, which transmits heat to a safety injection Closed Cooling Water System (CCWS). The CCWS transmits heat collected by the ECCS to an ultimate heat sink such as a river, cooling towers or the sea under post-LOCA or post-MSLB long-term cooling conditions.
The article entitled “In-Vessel Retention Enhancement through the Use of Nanofluids” describes using nanofluids for In-Vessel retention enhancement during an accident scenario. The conceptual nanofluid injection system includes two small tanks of concentrated nanofluid, with each tank capable of supplying enough nanofluid to provide enhancement predicted by a computational model. The injection is considered to occur upon the manual actuation of valves connected to injections lines. Instructions to actuate these valves are required to be placed in the severe accident procedures. The injection is said to be driven by gravity and overpressure provided by accumulators attached to the tanks. The injection lines are such that they can terminate in the reactor cavity, in the recirculation lines, or in the IRWST, depending on the physical space limitations within containment.
U.S. Pat. No. 6,724,854 describes the use of catalytic nanoparticles to high-temperature water systems to reduce stress corrosion cracking.